1. Field of the Invention
The present invention relates to a variable compression ratio internal combustion engine that changes the compression ratio of the internal combustion engine by changing the volume of a combustion chamber. In particular, it relates to a variable compression ratio internal combustion engine having a camshaft with a shaft member and a cam member fixed to the shaft member, and a movable bearing member rotatably fixed to the shaft member, wherein the camshaft is rotated to move a cylinder block and a crankcase toward and away from each other.
2. Description of the Related Art
In recent years, there has been proposed art capable of changing the compression ratio of an internal combustion engine for the purpose of improving fuel economy performance, output performance, and the like. Such art includes art in which a cylinder block and a crankcase are coupled with each other to enable relative movement therebetween, and camshafts are provided on the coupling portions thereof, the camshafts being rotated to cause relative movement between the cylinder block and the crankcase along the cylinder axial direction to change the volume of the combustion chamber and change the compression ratio. Such art is proposed in the Japanese Patent Application Publications Nos. JP-A-2003-206771 and JP-A-2005-113839.
In the foregoing art, however, the length of the movable bearing operating line segment, which is a line segment joining the center of the shaft member of the camshaft and the center of rotation of the movable bearing member in the bearing housing hole, is often equal to that of the cam operating line segment, which is the line segment joining the center of the shaft member of the camshaft and the center of rotation of the cam member in the cam housing hole.
In the above-described known configuration, depending upon the attitude of the movable bearing operating line segment and the cam operating line segment when the compression ratio of the internal combustion engine is changed, there are cases in which a force acting in the direction that moves the cylinder block and the crankshaft away from each other is amplified by combustion pressure in the internal combustion engine or the like in the direction of the movable bearing operating line segment and the cam operating line segment. When this occurs, deformation caused by the combustion pressure of the camshaft itself or the parts of the cylinder block or crankcase mated to the camshaft increases, and there is a risk of increased vibration of the internal combustion engine.